In the context of burners, fuels refer to fluids that store energy in forms that can be practicably released in exothermic reactions into heat energy. A burner is a device or a device arrangement by means of which these exothermic processes can be applied in a controlled combustion process.
A burner typically includes a nozzle that has an input for a fuel and for an oxidizing substance, and a carefully designed configuration of channels by means of which the fuel and the oxidizing substance are mixed into a combustible mixture and released into a combustion zone in front of the nozzle. Burners are usually divided into two main types, pre-mixed burners and post-mixed burners. In a pre-mixed burner the fuel and the oxidizing substance are completely mixed before they are discharged into the combustion zone. A post-mixed burner is one in which the fuel and oxidizing substance are kept separate until they are separately discharged into the combustion zone. A category of post-mixed burners is partially-aerated burners in which only a portion of the stoichiometric oxygen quantity that is necessary for complete combustion is mixed with the fuel before entry into the combustion zone. Additional secondary oxygen enters the flame after ignition to complete the process.
Pre-mixed burners are typically more effective, provide a more consistent flame than post-mixed burners, and for these advantages would be preferred in many application areas. For example, in surface treatment devices, pre-mixed burners are necessary to provide a uniform coating. However, it is understood that when a flammable mixture of fuel and air or oxygen is present in a gas volume upstream of the combustion zone, a flame can flash back into the gas volume that contains the pre-mixed flammable substances, and there is the possibility of an explosion due to uncontrolled rapid burning of flammable substances. Various mechanisms have been developed to arrest the flame and stop it from burning back up into the nozzle, but for safety reasons, post-mixed burners still tend to be preferred in many applications—even at the cost of performance. In applications where post-mixed burners are used, the limits for size where the nozzle must, for safety reasons, be kept are too small for many industrial applications, especially in the field of surface treatment devices.